<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <title>silder</title>
</head>
<style>

</style>

<body>
    <div class="wrap">

    </div>
    <script>
        var aLi = document.querySelectorAll(".box li");
        var box = document.querySelector('.box');
        var wrap = document.querySelector('.wrap');
        var aLiWidth = box.offsetWidth;
    </script>

</body>

</html>